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An officer and a weatherman

IT WAS a defining moment in British history. The Royal Navy’s victory over the French and Spanish fleets at the battle of Trafalgar elevated Admiral Nelson from national hero to legend, and gave its name to London’s grandest square and to hundreds of pubs up and down the country. Two centuries later, it has provided climatologist Dennis Wheeler with a victory of his own. The logbooks of the ships of Nelson’s fleet have helped him prove that seafarers’ observations of wind and weather, made long before ships carried reliable meteorological instruments, can give us a precise, daily record of the weather hundreds of years ago. That could be a key to understanding what is happening to the world’s climate today.

Climatologists and politicians are desperate to know whether the climatic changes the world is seeing now really are unprecedented, or whether there have been other times when change was just as swift. “If we go back to the past and find there really hasn’t been anything like this before, then that strengthens the case that human activity is responsible for the rapid changes we are seeing now,” says Wheeler, who shuttles between the University of Sunderland in north-east England and the National Maritime Museum at Greenwich in London.

But the past is tricky territory for climatologists. While tree rings and ice cores chart annual changes in climate going back millennia, they cannot show what happened from one month to the next. There are a few long-running records of temperature and air pressure dating back to the 17th century, but reliable data about air movements over the oceans – which govern …